1. Field of the Invention
The present invention relates to a spin-valve giant magnetoresistive head for reproducing magnetic information written in a minute single domain on a magnetic recording medium in a magnetic recording apparatus for use in a computer, an information processing apparatus and the like. In particular, the present invention relates to a spin-valve giant magnetoresistive head and its manufacturing method suitably used to prevent instability of magnetoresistive (MR) output voltage waveform caused by Barkhausen noise and obtain adequate MR output voltage, especially in a narrow-track head necessary to achieve high-density magnetic recording.
2. Description of the Related Art
a Thin-film magnetic head for writing and reading magnetic information is a key device to a magnetic recording apparatus. The thin-film magnetic head consists of a inductive write head for writing magnetic information and a read head for reading out the magnetic information written in a recording medium.
The read head for reading out the magnetic information from the recording medium includes a magnetoresistive element showing a resistance change to a very weak magnetic field applied from the outside, or a giant magnetoresistive element showing a resistance change larger than that of the magnetoresistive element. The reproducing head also includes a conductive film for supplying sensing current for use in sensing the resistance change.
The spin-valve giant magnetoresistive head that shows a large MR ratio to an applied magnetic field to produce a resistance change to a very weak magnetic field includes multiple thin films of giant magnetoresistive (GMR) sensor. The multiple thin films of GMR sensor are composed of at least an antiferromagnetic layer, a pinned magnetic layer, a free magnetic layer, a nonmagnetic conductive spacer that achieves magnetic insulation between the pinned magnetic layer and the free magnetic layer, and a nonmagnetic protective layer. The spin-valve giant magnetoresistive head also includes magnetic-domain control layers that maintain the magnetic orientation of the free magnetic layer in such a state that it intersects at right angles to that of the pinned magnetic layer. Further, the spin-valve giant magnetoresistive includes a conductive layer that supplies sensing current to the multiple thin films of GMR sensor to sense the resistance change.
In the spin-valve giant magnetoresistive head, a magnetic field necessary for magnetic-domain control is applied to the free magnetic layer to make a single domain of the free magnetic. This technique is important for preventing instability of MR output voltage waveform caused by Barkhausen noise.
FIG. 11 shows an exemplary cross-sectional structure of a conventional spin-valve giant magnetoresistive head as seen from the side opposite to magnetic recording media. First, a lower magnetic shield layer 41 is formed, and a lower insulated gap layer 42 is formed on the lower magnetic shield layer 41. Then, on the lower insulated gap layer 42, multiple thin films of GMR sensor D2 are formed in a trapezoidal cross-sectional shape. The multiple thin films of GMR sensor D2 are composed of an antiferromagnetic layer 1, a pinned magnetic layer 2 formed on the border of the antiferromagnetic layer so that its magnetic orientation can be aligned in a fixed direction, a free magnetic layer 4, a nonmagnetic conductive spacer 3 that achieves magnetic insulation between the pinned magnetic layer 2 and the free magnetic layer 4, and a nonmagnetic protective layer 5.
Magnetic-domain control layers 9 are formed on the side inclined parts of the multiple thin films of GMR sensor D2 and the lower insulated gap layer 42. The magnetic-domain control layers 9 make the magnetic orientation of the free magnetic layer 4 aligned in such a direction that it intersects at right angles to the magnetic orientation of the pinned magnetic layer 2. Base material layers 8 for the respective magnetic-domain control layers 9 are formed under the magnetic-domain control layers 9. Conductive layers 11 for supplying sensing current to the multiple thin films of GMR sensor to sense a magnetic resistance change are formed above the magnetic-domain control layers 9 through base material layers 10 for the respective conductive layers 11. An upper insulated gap layer 47 and an upper magnetic shield layer 48 are formed over the multiple thin films of GMR sensor D2 and the conductive layers 11.
In such a spin-valve giant magnetoresistive head, a magnetic field enough for magnetic-domain control is applied to the free magnetic layer 4, which makes it possible to prevent generation of Barkhausen noise, and hence instability of MR output voltage waveform. Thus a stable head can be provided.
One approach to reducing Barkhausen noise to prevent instability of MR output voltage waveform is described, for example, in JP-A-2000-215424. This publication presents such a structure that a flat part of a hard-bias layer having larger thickness than that of a free magnetic layer is positioned in the thickness direction of the free magnetic layer at the same level as the free magnetic layer. The free magnetic layer corresponds to the above-mentioned free magnetic layer 4. The generation of instable MR output, however, cannot be prevented by this approach alone.
It is an object of the present invention to provide a spin-valve giant magnetoresistive head and its manufacturing method capable of restraining instability of MR output voltage waveform.
To prevent generation of an instable MR output voltage waveform in a spin-valve giant magnetoresistive head, we directed our attention to the inclined angles of end parts of the free magnetic layer of end parts of multiple thin films of GMR sensor. We created spin-valve giant magnetoresistive heads with varied and inclined angles of end parts of the free magnetic layer of GMR sensor and measured the probability of occurrence of an instable MR output voltage waveform. Experimentally, it becomes apparent from the results of the measurement that variations in inclined angles of the end parts of the free magnetic layer of GMR sensor vary the probability of instability of MR output waveform caused by Barkhausen noise. It was found that the end parts of the multiple thin films of GMR sensor should be so made that the angle which the tangent line of each end inclined part to the middle line of the free magnetic layer in its thickness direction forms with respect to the middle line of the free magnetic layer is 45 degrees or more.
It is true that the tangent line of each inclined end part of the multiple thin films of GMR sensor to the middle line of the free magnetic layer in its thickness direction should form an angle of 45 degrees or more with respect to the middle line of the free magnetic layer, regardless of whether the antiferromagnetic layer in the giant magnetoresistive thin films is of one-layer or two-layer structure.
To make the inclined angles of the end parts of the free magnetic layer of the multiple thin films of GMR sensor form an angle of 45 degrees or more, after giant magnetoresistive thin films are formed, over etching is conducted onto the giant magnetoresistive thin films by ion milling or the like using a mask pattern such as a resist mask pattern. Thus the inclined end parts can form an angle of 45 degrees or more. The term xe2x80x9cover etchingxe2x80x9d denotes an etching process that takes a longer time than that required for etching of the above-mentioned giant magnetoresistive thin films. In this case, however, the lower magnetic gap film formed under the giant magnetoresistive thin films is also etched in this over etching process, the thickness of portions of the lower magnetic gap film directly under the openings of the photoresist mask pattern is reduced. The lower magnetic gap film is a nonmagnetic insulated film made of Al2O3 or SiO2 or both. As this film becomes thin, breakdown voltage between the film such as the magnetic-domain control layer or the conductive layer and the lower shield layer is made small, which runs the danger of reducing the performance of the magnetic head.
Experiments on this point revealed that the amount of reduction in the thickness of the portion between the magnetic-domain control layer and the lower shield layer relative to the thickness of the lower insulated gap film directly under the giant magnetoresistive thin films should be 10 nm maximum. In other words, the difference between the thickness of the portions of the lower insulated gap layer directly under the giant magnetoresistive thin films and the thickness of the lower insulated gap layer sandwiched between the magnetic-domain control layer and the lower shield layer should be 10 nm or less. This means that the amount of over etching in the process of forming the multiple thin films of GMR sensor should be 10 nm or less.
In the process of creating such multiple thin films of GMR sensor, it was also found that the thickness of the photoresist pattern as a mask material for the etching has a great effect on the complete shape. As a result, it became apparent that it would be better if the photoresist pattern is formed by laminating a 0.01 to 0.05 xcexcm thick organic film and a 0.1 to 0.35 xcexcm thick resist film.